The invention relates to a method and an apparatus for maintaining at a certain temperature, and for a certain period of time, a flow of a mixture of products consisting of a liquid of low to medium viscosity incorporating solid particles.
In continuous flow heating or cooling by means of heat exchangers (for example a tubular heat exchanger) of liquids of low to medium viscosity in which a certain volume percentage of solid particles is contained (for example a soup containing pieces of vegetables and meat), the transfer of heat is effected from the wall of the heat exchanger via the flowing liquid, the flow of which may or may not be turbulent, to the outer edge of the solid particles, and thence to the core of the latter. With this type of heat transfer the conveying liquid will have reached the desired final temperature far more quickly than the core of the solid particles entrained by the liquid. If for technical reasons connected with the process it is necessary for the core of the solid particles also to attain the same temperature as the liquid, the liquid and the solid particles must be kept at a constant end temperature for so long a time that differences in temperature between the liquid and the core of the solid particles are eliminated. This may have the consequence that the liquid remains for too long a time at the desired end temperature, so that (for example in the case of a food product) undesirable changes of taste and colour occur.
It is possible to subject the liquid and the solid particles separately to the desired heat treatment and to mix the two components together only after completion of the process or during the course of the latter. However, this necessitates two heat treatment installations in parallel, while in particular the plant required for the heat treatment of the solid particles is relatively complicated.